Spark plug electrode



Patented July 29, 1941 SPARK PLUG ELECTRODE Hugh S. Cooper, New York, N. Y., assignor to The American Steel and Wire Company of New J er-' sey, a corporation of New J ersey No Drawing. Application J anuary30 1940, Serial No. 316,447. In Great Britain March 14, 1939 Claims. (Cl. 123-169) This invention relates to electrodes, and particularly to an improved electrode for spark plugs and the like.

It is well known that when an electric discharge or are occurs between two pieces of metal or electrodes, the electrodes tend to burn. and wear away, and that when the discharge takes place in an atmosphere of rapidly moving and highly heated gases under pressure, as in the cylinder of an internal combustion engine, the wear on the electrodes of the spark plug therein is further aggravated by mechanical erosion. Such erosion of the electrodes in a spark plug results in a shortening.thereof,',thereby increasing the distance therebetween, until finally the distance between the electrodes becomes so great that the spark will not jump across the same and the spark plug fails.

Accordingly, it is one of the objects of the present invention to provide improved electrodes for spark plugs and the like in which the life thereof is materially increased thereby increasing the longevity ofthe spark plug.

It is another object of the invention to provide improved electrodes for spark plugs and the like in which the amount of erosion thereof is reduced to a minimum, thereby providing electrodes which last longer than any heretofore used.

It is 'a further object of this invention to protrode is prohibitive in that it is too expensive. Of the less expensivev metals and those that are commonly available, it has been found that nickel.

is the most satisfactory. Nickel electrodes are used either in the pure form or preferably they are alloyed with small percentages of silicon or other suitable metals and practically all of the electrodes used at present are made of nickel.

It might be presumed that to provide electrodes which will withstand erosion and burning, that,

' the electrode metal would necessarily have to be hard and oxidation-resistant, but this is erroneous, as actual tests have shown that such is not vide improved electrodes for spark plugs and the i like which are made from an inexpensive and durable metal, and, at the same time, of metal which is highly suitable for use as electrodes for spark plugs.

the case. As an example, pure nickel is neither hard, nor particularly resistant to oxidation, yet, of the non-precious and inexpensive metals it, has been found that this is the best metal adaptable for use as an electrode up until the present time. The properties that make a good electrode material therefore cannot be strictly defined in terms of other known properties or inferred from them, and can be determined'only by ei rperiment and use.

It has been found according to the present invention that an alloy of iron, chromium and silicon has the necessary properties required to make a good and satisfactory spark plug electrode. Such an alloy contains from 10 to percent chromium, and from 1 to 10 percent, of silicon, with the remainder being. substantially iron. Also, it is preferred that manganese up to 3 percent also be included in such an alloy. It

will be understood that the alloy may also contain without any ill effects small residues of any It is still-another object of the present invention to provide improved electrodes for spark plugs and the like made of metal between which the spark emcientlyand effectively discharges thereby providing a spark plug which fires efliciently at all times.

Various other objects and advantages of this invention will be more apparent in the course of the following specification and will be particu-,, larly pointed out in the appended claims.

The ability of an electrode to withstand combined gaseous erosion and the action of an electric arc depends on certain properties of the electrode metal, the exact nature of which has not been clearly ascertained by those skilled in the art. Various types of materials and metals have been suggested and used as electrodes in spark plugs. Of tho'sethat have been used, it has been found that platinum-iridium produces the best results, but the use of such a metal as an elecother deoxidizer, other than manganese, and fractional percentages of any of the materials commonly present as impurities in iron or steel.

Carbon .is one of the latter materials referred to and the carbon content in such alloy should be preferably below 0.10 percent for best results. It has been found through experiment and by 'tests, that the preferable composition of the alloy to provide an electrode for obtaining very satisfactory results contains approximately 25 percent chromium, approximately z percent silicon, and from [to 3 percent manganese with the remainder being preponderantly iron.

Numerous testshave been made with spark plugs having electrodes formed of an alloy of the present'invention and it has been-found that these electrodes possess. the specific and peculiar properties required of a successful spark plug electrode. In addition to possessing in a high degree the desirable and heretofore undisclosed properties of resisting erosion by heat peated electric arcing, the electrodes of the present .invention are easily workable and can therefore be riveted and headed, and are quite inexpensive in comparison with other electrodes of like or even inferior performance heretofore suggested and used.

As aresult oi. my invention, it will be seen that there is not only provided electrodes made 01' an alloy which is inexpensive and convenient to obtain and make, but also electrodes which inherently possess all the qualities and characteristics that are required of electrodes.

While I have described one embodiment of my invention, it will be understood that I do not wish to be limited exactly thereto, since various modifications may be made within the scope of my invention, as defined by the appended claims.

I claim:

1. An electrode for spark plugs and the like comprising an alloy consisting of from 10 to 30 percent ,chromium', from 1 to 10 percent silicon, and the remainder substantially pure iron.

gases, and resisting the destructive eflects of re- 2. An electrode for spark plugs and the like 1 comprising an alloy consisting of from 10 to 30 percent chromium, from 1 to 10 percent silicon, not over 8 percent manganese, and the remainder substantially pure iron.

3. An electrode for spark plugs and the like comprising an alloy consisting 01 from 10 to 30 percent chromium, from 1 to 10 percent silicon, notover 0.10 percent carbon, and the remainder substantially pure iron.

4. An electrode for spark plugs and the like comprising an alloy consisting of from 10 to 30 percent chromium, from '1 to 10.percent silicon, not over 3 percent manganese, not over 0.10 percent carbon, and the remainder substantially pure iron.

5. An electrode for spark plugs and the like comprising an alloy consisting of approximately 25 percent chromium, approximately 2 percent silicon, remainder substantially iron.

HUGH S. COOPER.

from 1 to 3 percent manganese, and the i 

